1. Field of the Invention
The present invention relates to an intake control device for an internal combustion engine.
2. Description of the Related Art
It is known that the amount of air to be drawn into the combustion chamber of an internal combustion engine may be increased using an inertia charging effect. Japanese Patent Application Publication No. 7-197823 (JP-A-7-197823) describes an intake control device for an internal combustion engine having two intake passages with different lengths from a surge tank to a combustion chamber and a passage length switching valve for switching the length of the intake passage from the surge tank to the combustion chamber depending on the operating condition of the internal combustion engine so that an inertia charging effect may be used to increase the amount of air to be drawn into the combustion chamber.
It is also known that the combustion is improved when the air drawn into the combustion chamber forms a tumble flow in the combustion chamber. The intake control device for an internal combustion engine described in JP-A-7-197823 has a tumble switching valve for forming a tumble flow of air in the combustion chamber in the intake passage upstream of the combustion chamber. When closed, the tumble switching valve partially closes the intake passage so that air can flow downstream along only one side of the tumble switching valve, that is, air flows downstream through only a portion of the intake passage to form a tumble flow of air into the combustion chamber.
The intake passage is partially closed by the tumble switching valve to form a tumble flow of air in the combustion chamber in the intake control device for an internal combustion engine described in JP-A-7-197823, whereas there is also an intake device, as described in, for example, Japanese Patent Application Publication No. 2002-70566 (JP-A-2002-70566), in which an intake passage is partitioned into two passages and one of the passages may be closed by a tumble control valve at the upstream end of the partition so that air flows into the combustion chamber only through the other path to form a tumble flow of air in the combustion chamber.
Also in the intake device described in JP-A-2002-70566, two intake passages with different lengths to the combustion chamber are formed and the length of the intake passage to the combustion chamber is switched with a variable intake length valve depending on the operating condition of the internal combustion engine so that an inertia charging effect can be used to increase the amount of air to be drawn into the combustion chamber as much as possible.
However, if a configuration in which an intake passage is divided into two passages by a partition and one of the passages may be closed by a tumble control valve at the upstream end of the partition to form a tumble flow of air in the combustion chamber is adopted, as in the intake device described in JP-A-2002-70566, even when the length of the intake passage to the combustion chamber is switched with the variable intake length valve in order to achieve an inertia charging effect, a sufficient inertia charging effect may not be achieved depending on the operating condition of the tumble control valve because the volume of the intake passage to the combustion chamber changes largely.